How Long Does a Loft Conversion Take? Week by Week

Quick answer: for a typical rear dormer loft in South West London, allow roughly four months from our first site visit to handover. Our standard programme runs: site visit in week 1, design and planning in weeks 2–4, a fixed-price quote in week 5, structural works in weeks 6–9, the dormer and roofing in weeks 9–12, interiors in weeks 12–16, then handover. The things that stretch it are a householder planning application (about eight weeks), a party wall dispute, or a more complex roof such as a hip-to-gable or mansard. Our Southfields dormer loft took 10 weeks on site.

"How long will it take?" is usually the second question after "how much?". The honest answer is that the build itself is fairly predictable once it starts. The time before it starts, for planning, party walls and building regulations, is where most programmes slip.

This guide splits the timeline into two parts: getting to a start date, and the build. It uses our own standard programme and our completed projects, and it explains what changes the timing in Wandsworth, Merton, Richmond, Lambeth and Hammersmith & Fulham.

Part 1: getting to a start date

Week 1: site visit

We visit, measure up, look at the roof structure, check head height and note any structural constraints. You get straight advice on what's achievable and what the next steps are. The site visit is free.

Weeks 2–4: design and the planning route

Your architect or ours develops the drawings. At this stage the planning route is fixed, and that decides most of the pre-build timing:

• Permitted development, confirmed by a Lawful Development Certificate. Outside conservation areas, many rear dormers fit Class B permitted development (40 m³ for a terrace, 50 m³ for a semi or detached house, counting earlier roof extensions). An LDC costs £274 from April 2026, and councils are expected to decide within eight weeks. You don't strictly have to wait for it, but most people do, because buyers' solicitors and lenders want to see it.
• Householder application. Needed in any conservation area (roof extensions aren't PD there) and for most mansards. The fee is £548 from April 2026, and most are decided within about eight weeks.

Our Lawful Development Certificate guide shows refusal rates by borough. In our Datahub pull, roughly one in seven proposed-use LDCs decided in the past year was refused in Wandsworth, Lambeth and Kingston, against about 4% in Merton. A refusal usually means a redesign and another wait of up to eight weeks, so getting the drawings right first time saves more time than anything else.

In parallel: party wall notices

On a terrace or semi, the steels for a loft usually bear on the party wall, so notices go to the neighbours. The Party Wall etc. Act requires notice before work starts, and each neighbour has 14 days to reply in writing. If they consent, there's no delay. If they don't, a dispute is deemed to have arisen and surveyors draw up an award, which adds weeks. Serve notices while the LDC or planning application is being decided. Our party wall timeline shows each step.

In parallel: building regulations

A full plans building regulations application should be decided within five weeks, or two months if you agree. The structural engineer's calculations and steel sizes go in with it. Ordering the steel is often the last thing that fixes the start date.

Week 5: fixed-price quote

Once the drawings are settled, you get a fully itemised quote covering every element of the build. Our fixed-price quote is based on the agreed written scope; client-requested changes and unforeseen work are priced and approved separately before proceeding.

Part 2: the build

Weeks 6–9: structure

The scaffold goes up, the roof is opened, steel beams go in and the new floor structure is formed. Our own team does this, not subcontractors. This is the noisiest stage, and the one where the house feels most like a building site.

Weeks 9–12: dormer and roof

The dormer structure is built, roof tiles or zinc are reinstated and rooflights fitted. The house is made weathertight before interior work begins. Once that's done, weather stops being a risk to the programme.

Weeks 12–16: interiors

The staircase is fitted, followed by plumbing and electrical first fix, insulation, plasterboard and plastering, then the bathroom, flooring and decoration. You get weekly updates throughout.

Week 16 onwards: handover

Final inspection, a snagging walk-through with you and building control sign-off. We come back at six weeks to complete any snagging list.

What our projects took

Project	Scope	Time on site
Southfields loft conversion, SW18	Full dormer loft, structural steelwork, insulation, rooflights, finishes	10 weeks
Wimbledon whole-house renovation, SW19	Whole-house renovation including a loft with shower room and a rear kitchen extension	25 weeks (whole project)
Chiswick townhouse, W4	Full refurbishment including a loft conversion	22 weeks (whole project)

The Southfields figure is the best guide for a stand-alone dormer loft. The other two show how much longer a programme runs when the loft is one part of a larger renovation.

What makes a loft take longer?

• Conservation areas. A householder application instead of an LDC. Wandsworth has 46 conservation areas, Lambeth 62, Richmond 85 and Hammersmith & Fulham 44, so this is common.
• Article 4 Directions. In Wandsworth's eight Article 4 areas, smaller roof changes such as re-roofing in a different material also need permission. Merton's John Innes Merton Park and Wilton Crescent areas and many Richmond streets have their own directions.
• Hip-to-gable or mansard roofs. More structure and more party wall work. See our hip-to-gable guide and mansard guide.
• Party wall disputes. Surveyors and an award add weeks before work can start.
• Changes during the build. Moving a bathroom or adding a window after the steel is ordered.
• A refused LDC. A redesign and a new application.

Living at home during a loft conversion

Most families stay in the house. Because the roof is opened from outside, using the scaffold, much of the early work happens without coming through the house. The disruption grows when the stair goes in, because that's when the loft is joined to the floor below, and when fire doors are fitted to the existing stairway. Plan for dust and noise on the first floor at that stage, and for some days with limited use of the landing.

How to keep your loft on programme

1. Check whether you're in a conservation area or Article 4 area before paying for drawings.
2. Fix the stair position before the dormer size.
3. Count any earlier roof extensions in the PD volume.
4. Serve party wall notices as soon as the structural design is settled.
5. Make your finish choices (bathroom, flooring, windows) before the interiors stage.
6. Agree any changes in writing, with the price, before the work is done.

Frequently asked questions

How long does a loft conversion take in London?

For a typical rear dormer, allow about four months from first site visit to handover. The build itself is usually around 10 weeks; our Southfields dormer loft took 10 weeks on site.

How long does planning take for a loft conversion?

A Lawful Development Certificate or a householder application is usually decided within about eight weeks. Party wall notices and building regulations can run alongside.

Can I live at home during a loft conversion?

Most families do. The early structural work is done from the scaffold. The most disruptive stage is when the stair goes in and the loft is joined to the floor below.

Does a hip-to-gable or mansard take longer?

Yes. Both involve more structure and party wall work than a rear dormer, and mansards usually need a householder planning application.

What's the most common cause of delay?

Pre-build approvals: a planning application where an LDC was expected, a refused LDC, or a party wall dispute.

Plan your loft with us

Bluebird Spaces is based in SW19 and is a member of the Federation of Master Builders. A typical loft conversion with us, a rear dormer with an en-suite, costs about £80,000–£90,000 to build, excluding VAT and professional fees (design, structural engineer, Building Control, party wall and planning fees); access and logistics can affect the final figure. See our loft conversion pages for Wimbledon, Wandsworth, Putney, Southfields, Earlsfield, Tooting, Balham and Richmond, then call 07564 041115 to book a free site visit.

Timings depend on the house and the approvals it needs. Always confirm the planning position with your council.